* To mensurate the hardness of microscope glass slide by utilizing Micro Hardness Tester. * To mensurate the hardness of Sintered Alumina Disk by utilizing Vickers Hardness Tester. * To determinate the facture stamina by utilizing the cleft lengths that obtains from both of the hardness trials. * To understand the different and relationship of glass and other ceramic stuffs.
The cost involved in mensurating ceramic-based stuffs is rather high. Hence. indenture techniques have been widely used to measuring the break stamina of brickle stuffs. In order to cipher the break stamina. hardness should be known by utilizing Micro Hardness Tester or Vickers hardness examiner.
The term Micro Hardness Test means the burden is non transcending 1 kgf when indenture is made. Normally. the indenter that be used is Vickers diamond pyramid and a level and polished sample surface is needed for this testing.
While the Vickers hardness trial method is use a burden of 1 to 100 kgf to the polished surface of the trial stuff. As the diagram shows below. since the force applied in the normal way. an included angle of 136 grades created between two faces that made during proving. The burden normally removed after force using for 10 to 15 seconds. and so a square form is formed on the level surface of ceramics. The length of two diagonals of this square can be measured by utilizing the examiner. which will be used in hardness computation.
The Vickers hardness can be calculated by utilizing load divide country of the square that obtained during the hardness testing.
Fracture stamina measuring
Fracture stamina is an built-in belongings of the stuffs. It describes ace opposition of a stuff.
During the break toughness measuring of ceramics. A Vickers indenture is pressed on a polished ceramic surface and clefts appeared around the indenture. The clefts are considered as the unreal defects and the length of it can be used to cipher the break stamina. The lengths of the clefts are in reverse proportion to the stamina and in direct proportion to lade applied.
The expression for ciphering the break stamina can be written as:
Microscope glass slide experiment
1. Take a fresh microscope glass slide. and avoid the fingerprint. 2. Put the glass slide simple in right place of the Micro Hardness Tester by utilizing a brace pincers. 3. Use a 1000g burden on the sample for 10 seconds to press an indenture and cleft on the surface of sample. 4. Measure the two diagonal lengths and two braces of cleft lengths. 5. Repeat the stairss 3 and 4 for one more clip. and cipher the norm of diagonal length and cleft length. 6. Repeat step3 to step5 to obtain diagonal length and cleft length at burden 500g. 300g. 200g. 100g.
Sintered aluminum oxide discs experiment
1. Take a sintered aluminum oxide sample. and avoid the fingerprint. 2. Put the sintered aluminum oxide simple in right place of the Vickers Hardness Tester by utilizing a brace pincers. 3. Use a 10kg burden on the sample for 10 seconds to press an indenture and cleft on the surface of sample. 4. Measure the two diagonal lengths and two braces of cleft lengths. 5. Repeat the stairss 3 and 4 for one more clip. and cipher the norm of diagonal length and cleft length. 6. Repeat step3 to step5 to obtain diagonal length and cleft length at burden 5kg. 3kg. 2kg. 1kg.
Observation & A ; Result
Equipment: Micro hardness TesterTest Sample: Microscope Glass Slide
Equipment: Vickers Hardness TesterTest Sample: Sintered Alumina Disk
Analysis & A ; treatment
1. For both glass and aluminum oxide specimens. secret plan the indenture burden ( P ) versus the square of the mean diagonal length ( d2 ) and take the incline of the consecutive line to determinate Hv in GPa ( Hint: the incline = Hv / 1. 8544 ) . For Microscope Glass Slide:
Harmonizing to the expression.
For Sintered Alumina Disk:
Lapp with the procedure of ciphering the Microscope Glass Slide
2. For both glass and aluminum oxide specimens. secret plan the indenture burden ( P ) versus the cleft length raised to the power of 3/2 ( i. e. c3/2 ) and take the incline of the consecutive line to determinate the KIc in MPam1/2 ( Hint: the incline = ( KIC / 0. 016 ) ( H/E ) 1/2. where H is the hardness Hv in GPa and E is the Young’s modulus in GPa. presuming E = 70 GPa for glass and E = 400 GPa for aluminum oxide ) .
a. Remark on the indenture method for measuring the break stamina of brickle stuffs by sing its utility and restrictions. The first restriction of the indenture method is that this method is non an equal tool to find clefts accurately. Cracks are difficult to be observed by conventional optical microscopes if the indenter burden is little and the material sample is thin. It’s because the breadth of the clefts is really narrow when the burden is excessively little to within the declaration of the conventional optical microscope. particularly near the tip of the clefts. During the glass slide experiment. the cleft length can non look when burden is 100g. We did five or six clip. merely one cleft length appeared. In add-on. the surface of ceramic substrates need to be level and polished before it uses to make the Vickers hardness proving. Since the break stamina is depend on the surface. if the surface did non polished good. it will impact the existent break stamina. However. it’s much cheaper and simple than other methods.
B. Compare the hardness and stamina values of glass with those of aluminum oxide. Explain the different mechanical belongingss in footings of atomic ( or Attic ) bonding and microstructure. Alumina as a non-silicate oxide ceramics. it forms an ionic compound since aluminium is a metal and O is non-metal. hence the bonding between them is ionic. Since aluminum oxide is form by ionic bonding. it has electrostatic attractive force between atoms. and the ions pack into a regular agreement. Hence. it gives them a comparatively high hardness but a low stamina.
While for glass. it is a alone ceramic. it depends on their atomic construction. Different with most other ceramics that have ordered crystalline construction. glass is extremely broken formless construction. In add-on. the most of spectacless are formed from silicon oxide ( SiO2 ) . which have tetrahedral unit that incorporate into ironss. Hence the hardness and stamina is lower than aluminum oxide.
c. The Young’s modulus should be given for a brickle stuff in order to find the stamina utilizing the indenture method. Describe three possible ways to mensurate the Young’s modulus. 1. Harmonizing to the definition of young’s modulus. there is:
Take one set of F and delta cubic decimeter informations in the additive potion of the stress-strain curve and submit in the above expression to obtain the young’s modulus. But sometimes. delta cubic decimeter is excessively little to mensurate. A system which used the contemplation rule of mirror is installed. harmonizing to ratio of the place of mirror. the distance between the mirror and admeasuring setup. every bit good as the delta l. it can convent the unmeasurable delta cubic decimeter to measurable delta Y which is the direct reading from wall or admeasuring setup.
2. See the force is jumping force alternatively of the force that applies. there is: . which can compare with Hooke’s jurisprudence:
3. There is.
Where Vs is the velocity of sound.
Yttrium is young’s modulus.
degree Fahrenheit is denseness of the stuff.
Which means the stiffer the stuff is. the faster the sound can go to the other terminal. and the larger young’s modulus is. Inversely. if the stuff is more elastic. it will take a longer clip for the sound reach the other terminal of the stuff and young’s modulus is lower.
For this experiment. it is really clear that chemical bonding and microstructure play an of import function in mechanical belongingss of ceramics. However. by and large. ceramics have high hardness and low stamina.
The normal glass is a really alone ceramic which is extremely formless construction. The belongingss of it may alter by adding other stuffs or do some other interventions.
The stamina may be non accurate due to the restriction of indenture method. In the existent state of affairs. although the indenture method is inexpensive and sample. other methods may be needed to obtain hardness and stamina.
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